Pug mills have been used for mixing particulate material for many years. Examples of such mills appear in U.S. Pat. Nos. 3,677,523 and 3,964,732. However, none of these mills nor any other prior art known to the inventor disclose the ability to both effectively mix and cool foundry or green molding sand.
The present invention teaches a new and unique combination of an apparatus for mixing molding sand, also called green sand, with a structure and process for keeping the molding sand within a desired predetermined temperature range and moisture content range.
Such improved control is extremely important since variations in the temperature and moisture content of the molding sand can greatly affect the characteristics of the molding sand to such an extent that the sand can become unusable if there is no accurate and thermodynamically correct method of controlling both the sands temperature and moisture content. Accordingly, it is a goal of the present invention to provide a process and a structure for accurately controlling the temperature and moisture content of the green sand.
The unique combination of structure and process of our present invention creates a cooling system that is very efficient and thus reduces the potential for too much or too little air being added to the sand. Too much air can dehydrate the bond and pull out bond and desirable fines from the sand. Further, excessive dehydration of the sand can reduce the moisture content to less than 1% and impede or make impossible cooling of the sand to the desired temperature. Too little air will result in the discharge of sand carrying too much moisture resulting in problems downstream; e.g. the sand could bind and become unflowable thereby creating a mold that is unpourable.
Consequently, it is a further objective of the present invention to produce a cooled mass of green foundry sand having an output or discharge temperature in the range of 90.degree. F. to 120.degree. F. and a discharge moisture content generally in the range of 1% to 3.5% where the present invention is processing sand at a rate of 100 tons per hour.
It is a further objective of the present invention to consistently produce sand having an output moisture content of substantially 2%.
Also, it is an objective of the present invention to be able to control the moisture content of the molding sand to within .+-.0.2% of a targeted moisture content; e.g. if the targeted moisture content were 2% then it would be desired to keep that range between 1.8% and 2.2%.
Finally, it is an objective of the present invention to control temperature of the output or discharge flow of the molding sand to .+-.5.degree. F.; e.g. if the goal temperature is 115.degree. F. then the temperature variation in the discharge sand would be between 110.degree. F. and 120.degree. F.